Step 1: Understanding the Concept:
This question asks about the belief of a secondary character, Mrs. Hall, regarding the strange events happening in her inn in the story "Footprints without Feet."
Step 2: Detailed Explanation:
When the invisible Griffin causes furniture to move on its own in his room at the inn, Mrs. Hall and the other villagers are terrified. The floating hat and the chair that springs to life and pushes her out of the room convince her that supernatural forces are at work. The text specifically mentions her thoughts: "My poor mother used to sit in that chair," she moaned. "To think it should rise up against me now!" The villagers thought it was witchcraft, and Mrs. Hall herself became hysterical, crying that the room was haunted by spirits. While 'ghosts' is a similar concept, 'spirits' is the word more directly associated with her reaction in the text.
Step 3: Final Answer:
Mrs. Hall was convinced that the room was haunted by spirits.